My Montana turns off routinely. Seems that there is only so many operations it can handle in a row. About 200 is my guess. When you hit this limit it switches off and a turn on resets what ever memory limit has been smashed. On a big day of caching this can happen enough times to be annoying.You can check the last error logs with the instructions from this page http://garminmontanagpsr.wikispaces.com/DiagnosticError Logs:Enter the Trip Computer application (Portrait screen orientation)Press and hold the lower right corner of the screen (over the Menu Bar) > 5 secondsA diagnostic screen will appear displaying a list of recently logged exceptionsThe lower section of the page will display current memory usage and statsSelect an exception from the list to view register dumps for that exceptionUse the back arrow to return to the list of exceptions and to exit this diagnostic mode